Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session F07: Nucleon Structure and Nucleon Spin |
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Chair: Julia Velkovska, Vanderbilt University Room: MG Salon G - 3rd Floor |
Sunday, April 16, 2023 8:30AM - 8:42AM |
F07.00001: Measurement of the Neutron Electromagnetic Form Factor at High Q2 Sean Jeffas The neutron electromagnetic form factors, GEn and GMn, give important insights into the neutron structure. In previous experiments the proton electromagnetic form factors, GEp, was measured up to Q2 = 8.5 GeV2, and GMp was measured up to Q2 = 30 GeV2, while GEn has only been measured up to Q2 = 3.4 GeV2. The Super BigBite Spectrometer (SBS) program at JLab will measure the neutron form factor ratio, GEn/GMn, at Q2 values of 2.9, 6.6, and 9.7 GeV2 by colliding a polarized electron beam with a polarized 3He target, used here as an effective polarized neutron target, and measuring the double spin asymmetry of the cross section. These measurements are scheduled to be completed in March of 2023 and preliminary analysis is underway. Early analysis of our 2.9 and 6.6 Q2 points will be presented. |
Sunday, April 16, 2023 8:42AM - 8:54AM |
F07.00002: N to Delta Transition Form Factors at low momentum transfers Hamza Atac, Nikos Sparveris, Michael E Paolone, RUONAN LI, Mark Jones, Mohammad Ali The first excited state of the nucleon dominates many nuclear phenomena at energies above the pion-production threshold and plays a prominent role in the physics of the strong interaction. The study of the N to Δ transition form factors (TFFs) allows to shed light on key aspects of the nucleonic structure that are essential for the complete understanding of the nucleon dynamics. In this talk we will discuss measurements of the TFFs in Hall C at JLab, utilizing the SHMS and the HMS spectrometers, that focus on low four-momentum transfer squared where the mesonic cloud dynamics are dominant and rapidly changing. |
Sunday, April 16, 2023 8:54AM - 9:06AM |
F07.00003: Determining the longitudinal double-spin asymmetry (ALL) for π0 production from STAR Emily Nelson The Solenoidal Tracker at RHIC (STAR) located at Brookhaven National Laboratory uses longitudinally polarized proton-proton collisions to study the gluon spin contribution to the known proton spin of ½ h-bar. The relative contributions of the quarks and gluons to the spin of the proton remain uncertain. Using data from the 2013 longitudinally polarized proton-proton collisions we study the asymmetry of proton spin-dependent production of neutral pions (π0s) from these collisions. π0s rapidly (8.5*10-17 s) decay into 2 photons that are detected by the Endcap Electromagnetic Calorimeter. By comparing the number of π0s produced when protons collide with different helicities, the asymmetry of π0 production (ALL), which can be related to the contribution of the gluon spin to the spin of the proton, can be measured. The two-photon invariant mass spectrum is reconstructed and then fit using a skewed Gaussian function to represent the π0 signal and a Chebyshev function to characterize the background. Various checks must be made to assure the quality of the data being analyzed. The status of this analysis will be presented. |
Sunday, April 16, 2023 9:06AM - 9:18AM |
F07.00004: Neutral pion multiplicity studies at CLAS12. Marshall Scott Multiplicity studies are a fundamental measurement of particle physics, detailing the production fraction of a particle species within a more general particle process. In the Semi Inclusive Deep Inelastic Scattering (SIDIS) process the hadron multiplicity studies use the production of hadrons from lepton-nucleon scattering to delve into the non-perturbative nature of the hadronization process. This process is the convolution of the perturbative electromagnetic hard scattering cross section, and the non-perturbative quark parton distribution and fragmentation functions. This work involves the SIDIS process at CLAS12, the CEBAF Large Acceptance Spectrometer for 12 GeV, where a 10.6 GeV electron beam was scattered off a fixed liquid hydrogen target in the Fall of 2018. We present the current status of the neutral pion multiplicity studies at CLAS12. |
Sunday, April 16, 2023 9:18AM - 9:30AM |
F07.00005: Single diffractive hard exclusive processes for the study of generalized parton distributions Zhite Yu, Jianwei Qiu Generalized parton distributions (GPDs) are important non-perturbative functions that provide tomographic images of partonic structures of hadrons. We introduce a type of exclusive processes for a better study of GPDs, which we refer to as single diffractive hard exclusive processes (SDHEPs), and give a general proof for their factorization into GPDs. We demonstrate that the SDHEP is not only sufficiently generic to cover all the known processes for extracting GPDs, but also well motivated for the search of new processes for the study of GPDs. We also examine the sensitivity of the SDHEP to the parton momentum fraction (x) dependence of GPDs, by examining two processes that can be readily measured at J-PARC and JLab, respectively. |
Sunday, April 16, 2023 9:30AM - 9:42AM |
F07.00006: Constraining the Polarized Gluon Distribution of the Nucleon with Experimental and Lattice Data Christopher Monahan, Nobuo Sato, Wally Melnitchouk, Kostas Orginos, Joe Karpie, Savvas Zafeiropoulos, Colin P Egerer, Jianwei Qiu, David G Richards, Robert Edwards Quantifying the partonic contributions to the spin of the proton has been a long-standing challenge for quantum chromodynamics (QCD), the theory of the strong nuclear force. The contribution from gluons, in particular, is still largely unknown, in part because the polarized gluon parton distribution function (PDF) is poorly constrained by current experimental data. We study the polarized gluon PDF of the nucleon through a Monte Carlo global QCD analysis of experimental data and pseudo-distributions determined from lattice QCD. We show that the inclusion of lattice QCD data helps constrain the behavior of the polarized gluon PDF at moderate values of Ioffe-time, demonstrating the importance of lattice QCD as a tool for understanding hadron structure, particularly for quantities that are poorly constrained by experimental data alone. |
Sunday, April 16, 2023 9:42AM - 9:54AM |
F07.00007: Measurement of the Weak Neutral Current Form Factor of the Proton at 2.5 (GeV/c)2 Caryn Palatchi The proposed COIN experiment at Jefferson Laboratory will determine the weak neutral current form-factor of the proton at 2.5 (GeV/c)2 via a measurement of the parity-violating asymmetry in elastic longitudinally polarized beam electron-proton scattering. The result will find or place an upper limit on the strangeness form factor at large momentum transfer. This is key to the flavor decomposition of u-quark and d-quark contributions to the nucleon form factors, which requires more stringent limits on possible strangeness contributions, well beyond those from existing data or lattice QCD calculations. Motivating this measurement is the experimental observation that u-quark and d-quark contributions to the Pauli and Dirac factors are nearly constant in ratio at low Q2, while the d-quark component drops relative to the u-quark component with increasing Q2 This measurement would present an important development in the experimental study of the strangeness content of the nucleon form factor flavor decomposition. |
Sunday, April 16, 2023 9:54AM - 10:06AM |
F07.00008: Physics informed deep learning models for deeply virtual exclusive processes Brandon Kriesten, Simonetta Liuti, Yaohang Li, Manal Almaeen, Huey-Wen Lin Deeply virtual exclusive reactions encode the dynamics of bound partons in hadrons through 3D quantum mechanical correlation functions - the generalized parton distributions; however, there are many steps in the analysis from experimental data to information on hadron structure. Currently, there is an immediate need to develop advanced phenomenology and computational tools in preparation for the exclusive reactions program planned for the upcoming EIC. The FemtoNet framework was developed to conduct an analysis of current exclusive experiments using physics-informed deep learning models in order to quantify information loss and reconstruction through the many inverse problems encountered. The FemtoNet framework simultaneously leverages a suite of uncertainty quantification techniques to separate epistemic (reducible) and aleatoric (irreducible) errors from the analysis and properly propagate experimental uncertainty. I will demonstrate what physics-informed deep neural networks are capable of in the context of reconstructing lost information from inverse problems in exclusive scattering experiments and give prospects for the future of such a program and consequences for an EIC. |
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